Using a synthetic route provided by NCI, the Contractor shall synthesize 30 grams of 4-Amino-1-((2R,4S,5R)-4-hydroxy-5-(hydroxymethyl)tetrahydrothiophen-2-yl)pyrimidin-2(1H)-one. Up to 650 grams of starting intermediate compound 1 will be provided by NCI toward completing this request. NCI requires that the synthesized material must have >98% HPLC purity with no more than 0.5% of any single impurity. NCI requires that the synthesized material must have a diasteromeric excess of greater than 99%.